fix: py3.9 typing syntax

Author: jorwoods

tableauserverclient/models/reference_item.py

@@ -1,8 +1,9 @@
+from typing import Optional
 from typing_extensions import Self
 
 
 class ResourceReference:
-    def __init__(self, id_: str | None, tag_name: str) -> None:
+    def __init__(self, id_: Optional[str], tag_name: str) -> None:
         self.id = id_
         self.tag_name = tag_name
 
@@ -20,11 +21,11 @@ def __hash__(self: Self) -> int:
         return hash((self.id, self.tag_name))
 
     @property
-    def id(self) -> str | None:
+    def id(self) -> Optional[str] :
         return self._id
 
     @id.setter
-    def id(self, value: str | None) -> None:
+    def id(self, value: Optional[str]) -> None:
         self._id = value
 
     @property